1. Field of the Invention
The present invention relates generally to satellite communication systems, and more generally to multi-port power amplifiers (“MPAs”) utilized in satellite communication systems.
2. Related Art
In today's modern society satellite communication systems have become common place. There are now numerous types of communication satellites in various orbits around the Earth transmitting and receiving huge amounts of information. Telecommunication satellites are utilized for microwave radio relay and mobile applications, such as, for example, communications to ships, vehicles, airplanes, personal mobile terminals, Internet data communication, television, and radio broadcasting. As a further example, with regard to Internet data communications, there is also a growing demand for in-flight Wi-Fi® Internet connectivity on transcontinental and domestic flights. Unfortunately, because of these applications, there is an ever increasing need for the utilization of more communication satellites and the increase of bandwidth capacity of each of these communication satellites.
In FIG. 1, a system diagram of an example of an implementation of a known communication satellite 100 is shown orbiting the Earth 102. In this example, the communication satellite 100 is shown orbiting the Earth 102 at distance 104 of about 36,000 kilometers (“km”) and illuminating part of the North American continent with a single beam 106 that results in a single satellite footprint 108 illuminating part of the North American continent. It is appreciated by those of ordinary skill in the art that the type of orbit and distance 104 of the communication satellite 100 may vary based on the mission and/or function of the communication satellite 100. For example, the communication satellite 100 may be a geostationary satellite that has an approximate constant distance 104 from the satellite footprint 108 (and a constant approximate 36,000 km distance from the equator of the Earth), a non-geostationary geosynchronous satellite that has an approximate constant distance 104 at a particular time each day, or a non-geosynchronous satellite (such as for example a low or medium Earth orbit satellite) that has a varying distance 104. Unfortunately, in this example the known communication satellite 100 is a single beam communication satellite with limited bandwidth capacity.
Known approaches to increase the bandwidth capacity utilize high level frequency re-use and/or spot beam technology which enables the frequency re-use across multiple narrowly focused spot beams. These known approaches typically involve the use of multi-beam communication satellite systems instead of a signal beam communication satellite 100 as shown in FIG. 1.
Turning to FIG. 2, a system diagram of an example of an implementation of a known multi-beam communication satellite 200 is shown orbiting the Earth 102. Unlike the example in FIG. 1, in this example the multi-beam communication satellite 200 is shown illuminating parts of the North American continent with multiple beams 202, 204, and 206 that result in multiple satellite footprints 208, 210, and 212, respectively, illuminating parts of the North American continent. The multi-beam communication satellite 200 is also shown orbiting the Earth 102 at a distance 214 that may also vary (as in the example of FIG. 1) based on whether the multi-beam communication satellite 200 is a geostationary satellite that has an approximate constant distance 214 from the footprints 208, 210, and 212, a non-geostationary geosynchronous satellite that has an approximate constant distance 214 at a particular time each day, or a non-geosynchronous satellite that has a varying distance 214. The multi-beam communication satellite 200 covers the same approximate combined footprint area (i.e., footprints 208, 210, and 212 combined) as the single footprint 108 of the single beam communication satellite 100, shown in FIG. 1. However, in this example, the multi-beam communication satellite 200 is capable of obtaining higher antenna gains in each individual beam 202, 204, and 206 than the antenna gain of the single beam 106 of the signal beam communication satellite 100. This results in the multi-beam communication satellite 200 having an improved equivalent isotropically radiated power (“EIRP”) and antenna gain-to-noise temperature (“G/T”), which results in improved bandwidth capacity.
Generally, these type of known multi-beam communication satellites 200 are effective for mobile communications or multi-media access networks because they have reduced transmitting power requirements and increased receiving power ability. However, these known systems do have a number of problems. As an example, their users may move from one geographic location to another and communication traffic may not be uniform among the multiple beams 202, 204, and 206 and may fluctuate over time. Moreover, generally these systems have insufficient beam 202, 204, and 206 isolation that may result in multi-path interference in the surrounding areas due to leakage through the adjacent beams 202, 204, and 206. As such, these types of multi-beam communication satellites 200 need a high power amplifier system that is capable of providing efficient transmitting power utilization with sufficient beam 202, 204, and 206 isolation.
At present, a well-known technique for providing this type of high power amplifier system is to utilize a multi-port power amplifier (“MPA”), also known as simply a “multi-port amplifier.” An MPA is a system that includes a power divider, power combiner, and an array of high power amplifiers (“HPAs”). In general, an MPA has a number N of similar HPAs in parallel, each having a power P, so that each input signal is amplified equally by each HPA, to potentially increase the power of an output signal by a factor N, to a total power equal to P multiplied by N. The N input ports and N output ports are provided, so that an input signal on one input port is routed to the corresponding output port. In general, the N is equal to the total number of input ports and output ports and also equal to 2n, where n is an integer equal to or greater than 2.
More specifically, in FIG. 3, a block diagram of an example of an implementation of a known MPA 300 is shown. The MPA 300 may include an input network which is an input hybrid matrix (“IHM”) 302, an output network which is an output hybrid matrix (“OHM”) 304, a plurality of tuning mechanisms 306, 308, and 310, and a plurality of high power amplifiers (“HPAs”) 312, 314, and 316. In this example, the IHM 302 includes input ports 318, 320, and 322 and the OHM 304 includes output ports 324, 326, and 328.
In this example, the IHM 302 is shown in signal communication with the tuning mechanisms 306, 308, and 310 via signal paths 330, 332, and 334, respectively. Similarly, The OHM 304 is shown in signal communication with the HPAs 312, 314, and 316 via signal paths 336, 338, and 340, respectively. The first tuning mechanism 306 is in signal communication with the first HPA 312 via signal path 342. Similarly, the second tuning mechanism 308 is in signal communication with the second HPA 314 via signal path 344. Moreover, the third tuning mechanism 310 is in signal communication with the third HPA 316 via signal path 346.
Further in this example, the IHM 302 is generally a power divider and the OHM 304 is generally a power combiner. As an example, the IHM 302 and OHM 304 may be two complementary N by N (i.e., N×N) Butler matrix networks that include a plurality of 90 degree hybrid networks (not shown). Additionally, each tuning mechanism 306, 308, and 310 is generally an equalizer and each HPA 312, 314, and 316 may be an amplifier unit such as, for example, a traveling wave tube amplifier (“TWTA”) or solid state amplifier. Specifically, each equalizer may provide, as a minimum, adjustment of gain and phase response and may also provide a single gain and phase adjustment, or multiple adjustments based on the frequency and amplitude of the intermediate signals provided by the IHM 302.
It is appreciated by those of ordinary skill in the art that in this example while only three (3) tuning mechanisms 306, 308, and 310, three (3) HPAs 312, 314, and 316, three (3) input ports 318, 320, and 322, and three (3) output ports 324, 326, and 328 output ports are shown, this number is for convenience of illustration and it is appreciated that there may be N tuning mechanisms, HPAs, input ports, and output ports. In general, each combination of tuning mechanism and HPA may be considered a HPA chain (resulting in a plurality of HPA chains 348) because it is appreciated that while each tuning element 306, 308, and 310 is shown prior to each HPAs 312, 314, and 316, respectively, in FIG. 3, the order may be optionally reversed with the reversed HPA chain still being functionally equivalent.
In general, MPAs have numerous advantages over classical amplification architectures (i.e., with one power amplifier per beam) provided that the operating point is carefully chosen. The MPA 300 allows the discrete amplifiers (i.e., the HPA 312, 314, and 316) to handle unbalanced traffic among beams and traffic variations over time while providing a common power pool.
In an example of operation, an input signal 350 may be injected into the first port 318 of the IHM 302 to produce an output signal 352 at the first output port 324. In any input signal injected into any of the input ports 318, 320, and 322 is divided into N intermediate signals 354, 356, and 358 that are passed to the tuning mechanisms 306, 308, and 310 and HPA 312, 314, and 316 chains. The N intermediate signals 354, 356, and 358 have particular phase relationships in that the first intermediate signal 352 may have a relative phase value of 0 degrees while the second intermediate signal 354 may have a relative phase value of 90 degrees.
As an example, if the IHM 302 is a 4 by 4 Butler matrix, there would be four (4) output intermediate signals (i.e., a first intermediate signal 354, second intermediate signal 356, a third intermediate signal (not shown), and a fourth intermediate signal 358) with varying phase values. As an example, the first intermediate signal 354 may have a relative phase value of 0 degrees and the second intermediate signal 356 may have a relative phase value of 90 degrees. The third intermediate signal may have a relative phase value of negative 90 degrees and the fourth intermediate signal 358 may have a relative phase value of 180 degrees. If the OHM 304 is also a 4 by 4 Butler matrix, the amplified and tuned intermediate signals would then be combined in a way that would result in first port 324 producing the output signal 352 that would be combination of all the tuned and amplified intermediate signals (i.e., the first intermediate signal 354, second intermediate signal 356, a third intermediate signal (not shown), and the fourth intermediate signal 358). The other output ports (i.e., second output port 326, third output port (not shown), and fourth output port 326) would not produce any output signals because they would be all phase cancelled out based on the respective phases of the four tuned and amplified intermediate signals.
Based on this, the advantage of utilizing an MPA is that it is an amplification architecture that provides intrinsic power flexibility since the power is shared between the channels (i.e., input ports 318, 320, and 322, the HPA chains 348, and output ports 324, 326, and 328). As such, the combined power of all the HPA chains 348 is available for any channel (i.e., output port 324, 326, and 328), provided that the other channels do not require power at the same time. This power flexibility is obtained without having to increase the power consumption.
Unfortunately, while very useful, MPAs have a number of inherent problems that affect their performance and therefore also affects the performance of the multi-beam communication satellite 200. Specifically, while the MPA 300 generally provides a pool of power that may be variably distributed among its multiple ports (i.e., channels), a drawback of MPAs is related to isolation losses between channels (i.e., the multiple ports 318, 320, and 322) due to different electrical characteristics of each path. Additionally, since all the input signals to the MPA 300 are amplified by each HPA 312, 314, and 316, multicarrier operation is reached even when a single carrier is introduced at each input port 318, 320, and 322.
Specifically, when the MPA 300 is free of errors, the various output signals 352, 360, and 362 exit the OHM 304 with complete isolation from each other; however, small errors anywhere within the MPA 300 may produce significant leakage of signals throughout the other (i.e., undesired) output ports. As an example, any errors in the MPA 300 may cause the desired output signal 352 to be leaked (as leakage signals 360 and 362) out of the other output ports 326 and 328 to produce a leakage of the output signal into the other ports 364.
As an example, some of these errors may be from the individual HPA 312, 314, and 316 that may introduce significant errors which will change over life, temperature and use of redundant or alternative units. The interconnecting transmission lines of signal paths 330, 332, 334, 336, 338, 340, 342, 344, and 346 and the imperfections in the tuning mechanisms 306, 308, and 310 may also contribute to the imbalance of the intermediate signals 354, 356, and 358 that may result in leakage throughout the MPA 300.
Known approaches for attempting to control MPA 300 alignment generally include two parts that include first providing mechanisms for tuning the MPA 300 adjustment and then determining the amount of adjustment to be made at each tuning mechanism 306, 308, and 310. Unfortunately, most of these known approaches require injecting special test signals into the MPA 300 input ports 318, 320, and 322 or at various interim locations internal (not shown) to the MPA 300, and then extracting the test signal from the output ports 324, 326, and 328. Often these approaches consume an output port 324, 326, and 328 of the MPA 300 for calibration purposes and the adjustments are often performed by trial-and-error, or by ad-hoc methods to minimize the leakage. Moreover, these approaches generally require extensive spacecraft hardware for making accurate measurements on the spacecraft and challenges still exist in directly measuring the phase and amplitude accurately from the ground.
Additionally, these approaches typically involve tuning the MPA 300 at a single frequency which generally only results in good performance near that specific frequency and is limited in maintaining that performance across a wide bandwidth of operation because of the varying frequency responses of each amplifier path (i.e., each signal path across each HPA of the HPA chains 348) across the bandwidth of operation. Moreover, these approaches generally require extensive spacecraft hardware for making accurate measurements on the spacecraft and challenges still exist in directly measuring the phase and amplitude accurately from the ground.
As such, there is a need for a system and method for making accurate phase and amplitude error corrections across a wide bandwidth of operation of an MPA so as to allow higher performance of the MPA across the wide bandwidth.